The present invention relates generally to semiconductor devices and, more specifically, to a cold-cathode device for emitting electrons in a field emission display and a method for forming the cold-cathode device.
A field emission display (FED) is a type of flat panel display that engineers have developed to replace the cathode ray tube (CRT) display. Typically, an FED includes a plurality of cathode emitter tips that can emit electrons while xe2x80x9ccold,xe2x80x9d i.e., not heated like the cathode coil of a CRT. These electrons collide with a cathodoluminescent material that coats the inner surface of a display screen. The electrons from each tip collide with the screen at a corresponding location or point. Each collision point forms all or part of a picture element, i.e., pixel, of a displayed image. The greater the collision rate at a particular pixel, the brighter the pixel appears. Likewise, the lower the collision rate, the dimmer the pixel appears. A screen that displays the image in color typically includes one pixel for each component color.
An active matrix FED, which has been described in the literature, includes a drive transistor that is formed as part of the FED. Thus, the active matrix provides faster pixel signal response times and more precise brightness and color control as opposed to passive matrix FEDs, which are driven by off-FED drive transistors.
Each cathode emitter tip of an active matrix FED is typically coupled to the electron receiving region of a drive transistor. That is, the tip is coupled to either the drain of a field effect transistor or the collector of a bipolar transistor. Often, the tip is formed directly on the electron receiving region. When the transistor is activated, i.e., turned on, electrons flow through the transistor and out of the tip toward the display screen. The greater the electron flow, i.e., current, through the tip, the greater the electron collision rate at the pixel associated with the tip, and thus the brighter the pixel.
Because it is physically disposed between the drive transistor and the display screen, the emitter tip typically is formed after the drive transistor. Forming the tip after forming the drive transistor may increase the complexity of the FED manufacturing process. Furthermore, the coupling between the tip and the electron receiving region of the drive transistor may weaken over time, and thus reduce the lifetime of the tip, i.e., the time during which the tip can effectively emit electrons.
In accordance with one aspect of the present invention, a cold-cathode emitter is provided. The cold-cathode emitter includes a high-voltage tank of a second conductivity that is formed in a substrate having a first conductivity. An emitter tip is integral with the tank and extends outwardly from the substrate. In a related aspect of the invention, the tip has a conical shape. In another related aspect of the invention, the tank forms either a drain region or a collector region of a transistor.
In accordance with another aspect of the present invention, a cold-cathode emitter device is provided. The device includes a drive transistor formed in a substrate of a first conductivity. The transistor includes an electron receive region of a second conductivity. An emitter tip is integral with the electron receive region and extends outwardly from the substrate. In a related aspect of the invention, the electron receive region forms a high-voltage tank. In another related aspect of the invention, the tip has a conical shape. In yet another related aspect of the invention, the transistor includes a source and a channel that is interposed between the electron receive region, which forms a drain of the transistor, and the source. Or, the transistor includes a transistor emitter and a transistor base that is interposed between the electron receive region, which forms a collector of the transistor, and the transistor emitter.
An advantage of the present invention is that the drive transistor and the emitter tip may be formed during the same process. Another advantage of the invention is that the emitter tip is integral with the electron receiving region of the drive transistor.
Still another advantage of the invention is that it takes advantage of the active matrix scheme, which provides a faster signal response at the emitter tip.